1. Field of the Invention
The present invention relates to Mach-Zehnder interferometer and method of making the same, more particularly, to single fiber Mach-Zehnder interferometer.
2. Description of the Related Art
Fiber in-line Mach-Zehnder interferometer (MZI) has various applications in optical fibers communication and optical fiber sensors. Various types of optical fiber in-line MZI structures have been developed, such as long period fiber grating (LPFG) and fiber with a tapered structure. LPFG includes structure with properties periodically varying along the fiber for guiding light from a guided mode to a cladding mode. The structure and the fabrication process for these devices are often complicated. Also, the size of these MZI devices can be relatively large.
Fiber in-line MZI based on interference between the guided modes of the fiber, including single mode fiber (SMF), multimode fiber (MMF) and photonic crystal fiber (PCF), have been used for temperature measurement and refractive index measurement. These devices typically include two cascading fiber components that function as beam splitter and combiner. The former converts part of the core mode power into a forward-propagating cladding mode and the latter recombines the two modes, resulting in a sharp interference. The commonly used “splitters/combiners” include long period gratings (LPGs), tapers, and sections of MMF or PCF.
However, these MZIs have relatively large size, in the order of millimeters or centimeters, and the highest temperature measured is limited to about 1000° C. Furthermore, these MZIs have relatively complex structures. Hence, there exists a need for a compact and simple single fiber MZI for applications such as high temperature and refractive index measurement.